Dielectric coating materials electrostatically deposited on articles comprise liquid droplets of paint formed from pigment, resinous binder and solvent or, simply, dry powder particles of pigment and resinous material. In each case, one of the major drawbacks of electrostatic deposition arises from the fact that not all of the particles which are directed towards an article to be coated are sufficiently electrostatically charged to be attracted to the article. These particles, and other charged particles which overshoot the article to be coated eventually settle on the floor of the installation. The resultant loss in deposition efficiency means that the effort expended in dispensing the particles which eventually finish on the floor of the installation is wasted. Moreover, where the particles represent droplets of liquid paint, deposition on the floor of the installation normally means that this expensive raw material is completely lost. Even where dry coating powders are used instead of paints, the powders deposited on the floor of the installation can only be re-used after expensive recovery operations.
Similar losses also occur when coating material particles are deposited on the side walls of the installation. However, this creates even more serious problems where the coating material consists of dry powder particles because, whenever it becomes necessary to change the colour of the coating material being dispensed, there is a possibility that coating material of a different colour which has already been deposited on the walls of the installation will be dislodged and transmitted into contact with the article to be coated, thereby causing the article to be at least partly coated with material of the wrong colour.